When the Editor has 2 Game windows opened and one of them shares a docked space with another window like Scene, the Game view doesn't recover (mouse input isn't recognized) when you switch to the shared tab and back when in Play mode.

Repro Steps:
1. Open the attached test project (case_1327556-EditorMouseInputBug.zip).
2. Click Play
3. Switch to Scene
4. Click into the separate Game Window.
5. Switch back to Game
6. Observe the Game tab you switched into doesn't recognize input.

Expected Results: The Game window recognizes mouse input and the ball goes red.
Actual Results: The Game window doesn't recognize the mouse input.

Reproducible with: 2020.3.5f1, 2021.2.0a15

Note:
- Recoverable if you click into the separated Game view then back into the one with the shared dock space.